ESR study of thianthrenium radical cation within acid zeolites

Thianthrene (E(OX) = 1.47 V vs NHE) has been adsorbed into a series of zeolites beta (beta) and ZSM-5 in the NH4+ or H+ forms, having different particle size and Si/Al ratio. The resulting population of generated thianthrenium radical cation was determined by a combination of diffuse reflectance and ESR spectroscopies. From the results obtained it can be concluded: i) the process takes predominantly place in the interior of the voids (XPS measurements and lack of influence of the particle size);)ZSM-5 is more efficient than zeolite beta; iii) no strong acid sites are required (both NH4+ and H+ forms produced very similar spin concentrations); iv) the zeolite framework acts isolating the organic spins, thus avoiding diamagnetic coupling (zeolite samples do obey Curie law); and v) the population of oxidizing sites increases with the aluminum content of the zeolite. (C) 1997 Elsevier Science Ltd.